Image sensor calibration system and method

Abstract

A calibration apparatus includes a calibration target such as a checkerboard, a frame configured to hold the checkerboard in place, a rotatable socket connected at one end to the frame, a stand which is connected to another end of the rotatable socket, a height adjusting portion connected at one end to the stand, and a platform connected to another end of the stand. The checkerboard can be tilted and moved to a particular distance and orientation with respect to an image system to be calibrated by the calibration apparatus. A method of identifying outlier images in the camera parameter estimation process, by using estimated 3D positions of the checkerboard compared with ground truth values.

1 . A calibration apparatus, comprising:
 a calibration target;   a frame configured to hold the calibration target in place;   a rotatable socket connected at one end to the frame;   a stand which is connected to another end of the rotatable socket;   a height adjusting portion connected at one end to the stand; and   a platform connected to another end of the stand,   wherein the calibration target can be tilted and moved to a particular distance and orientation with respect to an image sensor to be calibrated by the calibration apparatus.   
     
     
         2 . The calibration apparatus according to  claim 1 , wherein the rotatable socket comprises a universal joint. 
     
     
         3 . The calibration apparatus according to  claim 1 , wherein the height adjusting portion comprises separate telescoping elements that can be moved inwards and outwards with respect to each other. 
     
     
         4 . The calibration apparatus according to  claim 1 , further comprising:
 a plurality of wheels connected to a bottom surface of the platform,   wherein the calibration apparatus is movable to/from a device to be calibrated at different distances with respect to the device by way of rolling the calibration apparatus to appropriate locations with respect to the device.   
     
     
         5 . The calibration apparatus according to  claim 1 , wherein the calibration target comprises a checkerboard. 
     
     
         6 . A calibration apparatus, comprising:
 a movable platform;   a calibration target held on the movable platform;   a rotating unit configured to rotate the calibration target on the movable platform; and   a height adjusting unit configured to adjust a height of the calibration target on the movable platform,   wherein the calibration target can be tilted and moved to a particular distance and orientation with respect to an image sensor to be calibrated by the calibration apparatus.   
     
     
         7 . The calibration apparatus according to  claim 6 , wherein the calibration target comprises a checkerboard. 
     
     
         8 . A method of calibrating an imaging system of an apparatus, comprising:
 placing a calibration target mounted within a frame at a particular distance from the apparatus;   tilting the calibration target to a particular tilt angle with respect to the apparatus at the particular distance from the apparatus;   capturing image data obtained from the apparatus while the calibration target is at the particular distance from the apparatus and at the particular tilt angle;   moving the calibration target to at least one other distance from the apparatus;   tilting the calibration target to a particular tilt angle with respect to the apparatus at the one other distance from the apparatus; and   capturing image data obtained from the apparatus while the calibration target is at the one other distance from the apparatus and at the particular tilt angle.   
     
     
         9 . The method according to  claim 8 , wherein the tilting steps comprise:
 adjusting a rotatable joint connected to the frame so as to achieve the tilt of the calibration target at the particular tilt angle.   
     
     
         10 . The method according to  claim 8 , further comprising:
 adjusting a height of the calibration target while positioned at the particular distance from the apparatus, to be at a predetermined height with respect to ground.   
     
     
         11 . The method according to  claim 10 , wherein the adjusting comprises:
 manipulating a height adjusting portion connected to the calibration target so that the calibration target is positioned at the predetermined height with respect to ground.   
     
     
         12 . The method according to  claim 11 , wherein the height adjusting portion comprises a telescoping device. 
     
     
         13 . The method according to  claim 9 , wherein the rotatable joint comprises a universal joint. 
     
     
         14 . The method according to  claim 9 , wherein the calibration target comprises a checkerboard. 
     
     
         15 . An image calibration method, comprising:
 capturing predetermined images used during calibration at a plurality of predefined positions and orientations with respect to an imaging sensor to be calibrated;   based on the captured images at the plurality of predefined positions and orientations, forming a parameter set of images;   performing a calibration optimization process which includes obtaining a plurality of images at particular positions and orientations with respect to the imaging sensor to be calibrated; and   using the parameter set of images to determine whether any of the images obtained during the calibration optimization process are to be categorized as outlier images and thereby removed.   
     
     
         16 . The image calibration method according to  claim 15 , wherein an image is determined to be an outlier image when at least one of a position and an orientation of the image is greater than a predetermined distance and a predetermined orientation angle, respectively, with respect to any of the images that form the parameter set of images. 
     
     
         17 . The image calibration method according to  claim 15 , wherein an image is determined to be an outlier image when both a position and an orientation of the image is greater than a predetermined distance and a predetermined orientation angle, respectively, with respect to any of the images that form the parameter set of images.